Can you share more info on this? May be interested in doing this in 2020, but don’t want to open more credit cards. Were you able to get credit for the 15 nights without activating? Any other benefits to the zero fee cards that would make keeping it worthwhile?

Do you have your 20k US in spend? If so, don't spend money on a stay: take the cheapest stay on points (some are 15K) and just checkin. Nights stayed on points counts for stays in the 100 nights. But make sure that you have 20k in spend. I had to stay 120 nights before I hit 20k.